There are a number of different designs for commercial pressure cookers. One successful design is a pressurized rotary cooker, such as that described in U.S. Pat. No. 6,105,485, Zittel, hereby incorporated by reference. That design provides for a rotary blancher that is sealed such that it can be positively pressurized during operation to a pressure greater than the ambient pressure outside the blancher to increase food product heating speed and efficiency. The blancher (also called a pressure cooking section) has a sealed housing, a sealed food product inlet, and a sealed food product outlet all for enabling an atmosphere inside the blancher to be positively pressurized. A heat transfer fluid, such as a heated gas, a heated vapor, a heated liquid, or a combination thereof is introduced into the blancher to heat the food product inside the blancher. During operation, food products are continuously or substantially continuously introduced into the blancher through the food product inlet, continuously or substantially continuously processed by the blancher, and thereafter continuously or substantially continuously discharged from the blancher through the food product outlet.
Another design is shown in U.S. Pat. No. 8,087,348 and U.S. Pat. No. 8,776,674, both Maupin et al., both of which are hereby incorporated by reference. The design provides for a pressure vessel (also called a pressure cooking section) defining a compartment having an inlet end for receiving food product and an outlet end for discharging food product, an open-top screen mounted within the compartment and movable relative to the compartment between a first position, for food processing, and a second position, to facilitate cleaning, a rotatable auger mounted such that at least a portion of the auger is within the screen, the auger being operable to advance food product within the compartment from the inlet end of the pressure vessel toward the outlet end, and a transfer mechanism including a conduit in communication with the compartment, a fluid discharge positioned substantially within the conduit, and a pressurized fluid source in communication with the fluid discharge and operable to propel a fluid through the fluid discharge to move food product through the conduit.
Many prior art pressure cookers provided for an abrupt change in pressure/temperature to the product because the product was transferred from a low pressure/temperature area to the cooker which was a high pressure/temperature state. Then, after cooking the product again underwent an abrupt change in pressure and/or temperature because the product was transferred from the high pressure/temperature cooking section to a low pressure/temperature output section. Continuous cookers in particular provided abrupt pressure/temperature changes to product because the product moved continuously through the system.
Prior art continuous pressure cookers generally providing for transferring product into and out of a pressure cooking section using controllable valves at the input and output. Initially both valves are closed and the product staged for input (near the input valve. Then a valve at the entrance to an input spool chamber (isolating chamber) is opened to allow product into an un-pressurized spool chamber. The valve is closed after product is in the un-pressurized spool chamber. This means the product is in the spool chamber, but still not pressurized. A valve disposed between the spool chamber and the pressurized cooking section is opened to release the product into the pressurized cooking vessel. This thermally shocks the product. The lower valve closes so both valves are again closed, and then the spool section is vented (for safety reasons) before the input valve is again opened. These steps are performed rapidly in the prior art.
The discharge of product from prior art continuous pressure cookers is similarly accomplished. An output spool section has valves disposed between the spool section and the cooking section, and between the spool section and the output section. Initially both valves closed and the product is staged in the cooking section for being provided to the output spool section. Then, the valve between the cooking section and output spool section is opened, to allow product from pressure vessel to move into the un-pressurized spool chamber. Thus, the product abruptly goes to a chamber a temperature and pressure lower than that of the cooking section. While the pressure in the output spool section equalizes with the pressure in the cooking section, there change does have an effect on product. Next, the valve between the cooking section and output spool section is closed and the pressure in the spool section is slowly vented and cooling water added. The valve between the spool section and the output section is opened to release product, and then the valve is closed so that both valves are again closed.
Prior art pressure cookers have abrupt temperature/pressure changes and were used primarily to cook products that were relatively durable, and could withstand the relatively rapid decompression at the discharge of product (such as from a continuous rotary valve), or the slight decompression that comes with an isolating chamber. Indeed, depressurization has been used in the prior art to peel products, and produce and fracture some products such as pinto beans for refried beans.
However, the same forces that can be used to peel or fracture products can damage products that are fragile and/or have easily damaged skins. For examples whole dry beans cooked in prior art continuous pressure cookers result in split beans or poor product integrity because water under the skin of the beans can to flash to steam during depressurization.
Accordingly, a continuous pressure cooker that provides for less abrupt changes in pressure and/or temperature as the product enters and/or exits the pressurized cooking section is desirable. Preferably, such a continuous pressure cooker will be able to cook products that are fragile and/or have easily damaged skins.